Memory device with charge-recycling arrangement and method of operating the same

ABSTRACT

A method (for recycling charge from a first bit line of a memory device to a second bit line of the memory device) includes: before pre-filling the second bit line, momentarily closing switches to transfer a first charge from the first bit line which is involved in a first read operation to the second bit line which is involved subsequently in a second read operation; and each of the first bit line and the second bit line being served by a same sense amplifier.

PRIORITY CLAIM

The present application is a continuation of U.S. application Ser. No.17/341,930, filed Jun. 8, 2021, which is a continuation of U.S.application Ser. No. 16/698,552, filed Nov. 27, 2019, now U.S. Pat. No.11,031,051, issued Jun. 8, 2021, which is a continuation of U.S.application Ser. No. 16/207,009, filed Nov. 30, 2018, now U.S. Pat. No.10,497,407, issued Dec. 3, 2019, which is a continuation of U.S.application Ser. No. 15/877,034, filed Jan. 22, 2018, now U.S. Pat. No.10,147,469, issued Dec. 4, 2018, which is a continuation of U.S.application Ser. No. 15/460,687, filed Mar. 16, 2017, now U.S. Pat. No.9,875,774, issued Jan. 23, 2018, which claims the priority of U.S.Provisional Application No. 62/427,700, filed Nov. 29, 2016, which areincorporated herein by reference in their entireties.

BACKGROUND

A memory device includes: an array of memory cells (which areprogrammable) and a corresponding array of reference memory cells(‘memory_bar cells’); a sense amplifier; first and second branched linesconnected to corresponding first and second input terminals of the senseamplifier; and an arrangement of bit lines and bit_bar lines which arecontrollable to selectively connect one of the memory cells and acorresponding one of the memory_bar cells to the first and secondbranched lines.

A read operation of the sense amplifier includes three modes (as listedin the order of occurrence): a precharge mode; an evaluation mode; and adischarge mode. In the precharge mode, the first and second branchedlines are precharged by the sense amplifier. In the discharge mode, thefirst and second branched lines and a selected one of the bit lines anda corresponding selected one of the bit_bar lines are connected (andthus discharged) to ground. Of the total energy consumed by the senseamplifier, a large portion is attributable to the read operation.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 is a block diagram of a semiconductor device, in accordance withat least one embodiment of the present disclosure.

FIG. 2 is a diagram of a read-operation phase-flow for a memory device,in accordance with at least one embodiment of the present disclosure.

FIGS. 3A-3J are block diagrams of a memory device at correspondingphases of read operations, in accordance with at least one embodiment ofthe present disclosure.

FIG. 4 is a flowchart of a method of reading data from a memory cell, inaccordance with at least one embodiment of the present disclosure.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components, values, operations, materials,arrangements, or the like, are described below to simplify the presentdisclosure. These are, of course, merely examples and are not intendedto be limiting. Other components, values, operations, materials,arrangements, or the like, are contemplated. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

The present disclosure, in various embodiments, is generally related toa memory device and method of operating the memory device which recyclescharge in order to reduce energy consumption during a read operation. Insome embodiments, during a recovery phase, first and second charges arerecovered (into corresponding first and second capacitors)correspondingly from the selected bit line and the correspondingselected bit_bar line before a drainage phase in which the selected bitline and the corresponding selected bit_bar line are drained to ground.Such a recovery phase has a benefit of reducing amounts of charge whichwould otherwise be drained to ground, which reduces energy wasted duringthe subsequent drainage phase, and thus during the read operation. Insome embodiments, during a reuse phase, the first and second charges arereused (transferred out of the corresponding first and secondcapacitors) onto the corresponding first and second branched linesbefore a pre-fill phase in which the first and second branched lines arepre-filled (to a level of a reference voltage) by the sense amplifier.Such a reuse phase has a benefit of reducing amounts of charge which thesense-amplifier would otherwise provide in order to reach the referencevoltage on the corresponding first and second branched lines, whichreduces energy consumed during the subsequent pre-fill phase, and thusduring the read operation.

FIG. 1 is a block diagram of a semiconductor device 100, in accordancewith at least one embodiment of the present disclosure.

Semiconductor device 100 includes a memory 101 and a controller 150.Memory device 101 is similar to memory device 301 of FIGS. 3A-3J (whichis described in detail below). Memory device 101 includes: a senseamplifier 103; terminal switches 106A-106B; branch lines 109A-109B; amultiplexer 110; a first array of bit lines B_Line(0)-B_Line(N-1) and acorresponding second array of bit_bar linesB_bar_Line(0)-B_bar_Line(N-1), where N is a positive integer and N≥2; amultiplexer 120; a first recycling arrangement 130A; and a secondrecycling arrangement 130B. For the sake of brevity of description, thediscussion of FIG. 1 will focus on differences between FIG. 1 and FIGS.3A-3J (again, described below).

Memory device 301 includes a first array 144 of memory cells and acorresponding second array 146 of reference memory cells (again,‘memory_bar cells’). A first array of bit lines B_Line(0)-B_Line(N-1) isshown as connecting to array 144 of memory cells. A second array ofbit_bar lines B_bar_Line(0)-B_bar_Line(N-1) is shown as connecting toarray 146 of memory_bar cells. In some embodiments, controller 150generates control signals CTRL_108A, CTRL_108B,CTRL_114A(0)-CTRL_114A(N-1), CTRL 124A(0)-CTRL 124A(N-1), CTRL114B(0)-CTRL 114B (N-1), CTRL 124B(0)-CTRL_124B(N-1),CTRL_134A-CTRL134B, and CTRL_134A_bar & CTRL134B_bar so as to implementphases 302A-302J of read operations of corresponding FIGS. 3A-3J(discussed below).

FIG. 2 is a diagram of a read-operation phase-flow 200 for a memorydevice (not illustrated in FIG. 2 ), in accordance with at least oneembodiment of the present disclosure. Additional phases can be providedbefore, during, and/or after the phase-flow 200.

In FIG. 2 , for simplicity of illustration, two read operations 202A and202B are shown in phase-flow 200. In some embodiments, other quantitiesof read operations are included in phase-flow 200.

FIG. 2 assumes a context in which the memory device (not illustrated inFIG. 2 ) includes: an array of memory cells (which are programmable) anda corresponding array of reference memory cells (‘memory_bar cells’); asense amplifier; first and second branched lines connected tocorresponding first and second input terminals of the sense amplifier;an arrangement of bit lines and bit_bar lines which are controllable toselectively connect one of the memory cells and a corresponding one ofthe memory_bar cells to the first and second branched lines; and firstand second capacitors selectively connectable to the first and secondbranched lines. Also, for simplicity of illustration, read operations202A and 202B are labeled ‘bit line’ in corresponding phases 204A, 204B,214A, and 214B. It is to be understood that each phase in phase-flow 200concerns not only a selected one of the bit lines and/or thecorresponding first branched line, but also the selected one of thecorresponding bit_bar lines and/or or the corresponding second branchedline.

Read operation 202A includes: a bit line pre-boost phase 204A; anevaluation phase 206A which follows bit line pre-boost phase 204A; and adischarge phase 210A which follows evaluation phase 206A. Similarly,read operation 202B includes: a bit line pre-boost phase 204B; anevaluation phase 206B which follows bit line pre-boost phase 204B; and adischarge phase 210B which follows evaluation phase 206B. In someembodiments, read operations 202A-202B are instances of a cyclic generalread cycle.

The sense amplifier (103 in FIG. 1 ) is configured, in evaluation phase206A to compare voltages provided by a selected one of the memory cells(as connected through a corresponding one of the bit lines and the firstbranched line) and a corresponding selected one of the memory_bar cells(as connected through a corresponding one of the bit_bar lines and thesecond branched line). Based on the comparison, the sense amplifiergenerates an output indicating a particular logic state stored in theselectively connected one of the memory cells. In phase-flow 200, theoutput of read operation 202A is shown as a pulse 208A of data, and theoutput of read operation 202B is shown as a pulse 208B of data.

In contrast to another precharge mode, pre-boost phase 204A according toan embodiment includes two phases, namely a reuse phase 212A and a bitline pre-fill phase 214A. Similarly, pre-boost phase 204B includes twophases, namely a reuse phase 212B and a bit line pre-fill phase 214B.

In some embodiments, during reuse phase 212A, first and second chargesin the first and second capacitors are reused (transferred out of thecorresponding first and second capacitors) onto the corresponding firstand second branched lines before pre-fill phase 214A in which the firstand second branched lines are pre-filled (to a level of a referencevoltage) by the sense amplifier. For brevity, a corresponding discussionof reuse phase 212B is omitted here (but see the discussion below). Eachof reuse phases 212A-212B has a benefit of reducing amounts of chargewhich the sense-amplifier would otherwise provide in order to reach thereference voltage on the corresponding first and second branched lines,which reduces energy consumed subsequently during corresponding pre-fillphases 214A-214B, and thus during the read operation. Whereas a readoperation by a sense amplifier according to another approach wouldinclude three modes (precharge, evaluate and discharge) and wouldprovide an amount of charge PC during the precharge mode of the otherapproach (where PC represents about 67.5% of the total charge consumedduring the read operation according to the other approach), during apre-fill phase according to an embodiment, e.g., pre-fill phase 214A,the sense amplifier provides an amount of charge PB, where PB<PC.

In terms of delay, it is noted that though the singular precharge modeof other approaches is replaced by two phases in accordance with anembodiment, e.g., reuse phase 212A and pre-fill phase 214A, becausereuse phase 212A reduces the amount of charge which the sense-amplifierprovides subsequently during pre-fill phase 214A, the length of timeneeded by the sense amplifier in which to provide the reduced amount ofcharge during pre-fill phase 214A is shorter than the duration of thesingular precharge mode of the other approaches. The time saved by theshorter pre-fill phase 214A according to an embodiment, when combinedwith the length of time needed to complete reuse phase 212A is typicallyno longer than the duration of the precharge mode of the otherapproaches. In some embodiments, the aggregate time for reuse phase 212Aand pre-fill phase 214A according to an embodiment is smaller than theduration of the precharge mode of the other approaches.

In contrast to a discharge mode of other approaches, discharge phase210A according to an embodiment includes two phases, namely, a recoverphase 216A and a drainage phase 218A. Similarly, discharge phase 210Bincludes two phases, namely, a recover phase 216B and a drainage phase218B.

In some embodiments, during recovery phase 216A, charges are gleanedresulting in gleaned charges, e.g., first and second charges arerecovered (into the corresponding first and second capacitors)correspondingly from (A) the selected bit line and the first branchedline and (B) the corresponding selected bit_bar line and the secondbranched line before drainage phase 218A in which (A) the selected bitline and the first branched line and (B) the corresponding selectedbit_bar line and the second branched line are drained to ground. Forbrevity, a discussion of drainage phase 218B is omitted here (but seethe discussion below). Each of recovery phases 216A-216B has a benefitof reducing amounts of charge which would otherwise be drained toground, which reduces energy wasted during the subsequent drainagephase, and thus during the read operation.

In terms of delay, it is noted that though the singular discharge modeof other approaches is replaced by two phases in accordance with anembodiment, e.g., recover phase 216A and drainage phase 218A, becauserecover phase 216A reduces the amount of charge which is drained toground subsequently during drainage phase 218A, the length of timeneeded in which to drain charge to ground during drainage phase 218A inaccordance with an embodiment is shorter than the duration of thedischarge mode of the other approaches. The time saved by the shorterdrainage phase 218A in accordance with an embodiment, when combined withthe length of time needed to complete recover phase 216A is typically nolonger than the duration of the discharge mode of the other approaches.In some embodiments, the aggregate time for recover phase 216A anddrainage phase 218A in accordance with an embodiment is smaller than theduration of the discharge mode of the other approaches.

FIGS. 3A-3J are block diagrams of a memory device 301 at correspondingphases 302A-302J of read operations, in accordance with at least oneembodiment of the present disclosure. Reference numerals in FIGS. 3A-3Jcorrespond to reference numerals in FIG. 1 albeit increased by 300.

Generally, in FIGS. 3A-3J, read operations phases 302A-302J correspond,e.g., to phases 214A, 206A, 216A-218A, 212B-214B, 206B, 216B-218B and212A of FIG. 2 .

In FIG. 3A, memory device 201 is shown in pre-fill phase 302A, whichcorresponds, e.g., to pre-fill phase 214A of FIG. 2 .

Memory device 301 includes: a sense amplifier 303; terminal switches306A-306B; branch lines 309A-309B; a multiplexer 310; a first array ofbit lines B_Line(0)-B_Line(N-1) and a corresponding second array ofbit_bar lines B_bar_Line(0)-B_bar_Line(N-1), where N is a positiveinteger and N≥2; a multiplexer 320; and capacitors 336A-336B. Senseamplifier 303 has input terminals 304A-304B and an output terminal 304C.Sense amplifier 303 includes a precharge circuit (138 in FIG. 1 ) and anevaluation circuit (140 in FIG. 1 ). In some embodiments, senseamplifier 303 is a differential amplifier. In some embodiments, senseamplifier 303 is a non-differential amplifier. Bit linesB_Line(0)-B_Line(N-1) are connected to corresponding memory cells (array144 in FIG. 1 ). Bit_bar lines B_bar_Line(0)-B_bar_Line(N-1) areconnected to corresponding memory_bar cells (array 146 in FIG. 1 ).

Terminal switches 306A-306B are: connected between correspondingterminals 304A-304B and corresponding branched lines 309A-309B; and arecontrolled by corresponding control signals CTRL_308A-CTRL_308B.Terminal switch 306A is connected between terminal 304A and branchedline 309A. Terminal switch 306A is controlled by control signalCTRL_308A. Terminal switch 306B is similarly connected with terminal304B and branched line 309B. Terminal switch 306B is controlled bycontrol signal CTRL_308B. Multiplexer 310 is organized into a first bank311A and a second bank 311B. Bank 311A of multiplexer 310 is connectedbetween branched line 309A and a first array of bit linesB_Line(0)-B_Line(N-1). Bank 311B of multiplexer 310 is connected betweenbranched line 309B and a second array of bit_bar linesB_bar_Line(0)-B_bar_Line(N-1). In some embodiments, multiplexer 310 isreplaced by two multiplexers, a first one of the multiplexerscorresponding to bank 311A, and a second one of the multiplexerscorresponding to bank 311B.

Bank 311A of multiplexer 310 includes leg switches 312A(0)-312A(N-1).Bank 311B of multiplexer 310 includes leg switches 312B(0)-312B(N-1).Leg switches 312A(0)-312A(N-1) and 312B(0)-312B(N-1) are controlled bycorresponding control signals CTRL_314A(0)-CTRL_314A(N-1) andCTRL_314B(0)-CTRL_314B(N-1).

Multiplexer 320 is organized into a first bank 321A and a second bank321B. Bank 321A is connected between bit lines B_Line(0)-B_Line(N-1) andground. Bank 321B is connected between bit_bar linesB_bar_Line(0)-B_bar_Line(N-1) and ground. In some embodiments,multiplexer 320 is replaced by two multiplexers, a first one of themultiplexers corresponding to bank 321A, and a second one of themultiplexers corresponding to bank 321B.

Bank 321A of multiplexer 320 includes drain switches 322A(0)-322A(N-1).Bank 321B of multiplexer 320 includes drain switches 322B(0)-322B(N-1).Drain switches 322A(0)-322A(N-1) and 322B(0)-322B(N-1) are controlled bycorresponding control signals CTRL_324A(0)-CTRL_324A(N-1) andCTRL_324B(0)-CTRL_324B(N-1).

Memory device 301 also includes recycle switches 332A-332B and drainswitches 333A-333B. Together, recycle switch 332A, drain switch 333A andcapacitor 336A comprise a first recycling arrangement 330A. Together,recycle switch 332B, drain switch 333B and capacitor 336B comprise asecond recycling arrangement 330B.

Recycle switches 332A-332B, which include corresponding controlterminals, are controlled by corresponding control signals CTRL_334A andCTRL_334B. Drain switches 333A-333B are controlled by correspondingcontrol signals CTRL_334A_bar and CTRL_334B_bar. In some embodiments,control signals control signals CTRL_334A_bar and CTRL_334B_bar are theinverse of corresponding control signals CTRL_334A and CTRL_334B. Firstterminals of recycle switches 332A-332B are connected at correspondingnodes 340A-340B to corresponding branched lines 309A-309B. Secondterminals of recycle switches 332A-332B are connected at correspondingnodes 342A-342B to first plates of corresponding capacitors 336A-336B.Second plates of capacitors 336A-336B are connected to ground. Firstterminals of drain switches 333A-333B are connected at correspondingnodes 342A-342B to first plates of corresponding capacitors 336A-336B.Second terminals of drain switches 333A-333B are connected to ground.

Parasitic capacitance of branched line 309A alone or when connected to aselected one of bit lines B_Line(0)-B_Line(N-1) is represented by acapacitor 336A connected between branched line 309A and ground.Parasitic capacitance of branched line 309B alone or when connected to aselected one of bit_bar lines B_bar_Line(0)-B_bar_Line(N-1) isrepresented by a capacitor 336B connected between branched line 309A andground. Details regarding arrangements and read operations of memorydevices, in general, are found in U.S. Pat. No. 8,964,485, granted Feb.24, 2015, and U.S. Pat. No. 6,903,436, granted Jun. 7, 2005, theentirety of each of which is hereby incorporated by reference.

In pre-fill phase 302A, all drain switches 322A(0)-322A(N-1) and322B(0)-322B(N-1) are controlled to be open, thereby disconnecting bitlines B_Line(0)-B_Line(N-1) and bit_bar linesB_bar_Line(0)-B_bar_Line(N-1) from ground. Leg switches 312A(0) and312B(0) are controlled to be closed, thereby connecting bit lineB_Line(0) and bit_bar line B_bar_Line(0) to corresponding branched lines309A-309B. Also, leg switches 312A(1)-312A(N-1) and 312B(1)-312B(N-1)are controlled to be open, thereby disconnecting bit linesB_Line(1)-B_Line(N-1) and bit_bar lines B_bar_Line(1)-B_bar_Line(N-1)from corresponding branched lines 309A-309B.

Furthermore, in pre-fill phase 302A, recycle switches 332A-332B arecontrolled to be open, thereby disconnecting capacitors 336A-336B fromcorresponding branched lines 309A-309B. Also, terminal switches306A-306B are controlled to be closed, thereby connecting terminals304A-304B of sense amplifier 303 at corresponding nodes 340A-340B tocorresponding branched lines 309A-309B. As such, in pre-fill phase 302A,sense amplifier 304A provides amounts of charge to adjust voltages oncorresponding branched lines 309A-309B to a level of a referencevoltage.

During pre-fill phase 302A, the precharge circuit (138 in FIG. 1 ) insense amplifier 303 provides the noted amounts of charge. Leg switches312A(0) and 312B(0) are controlled to be closed. Consequently, aresultant charge and a resultant_bar charge accumulate on thecorresponding first and second line pairs and thus at correspondingterminals 304A-304B of sense amplifier 303.

Assuming that pre-fill phase 302A follows a reuse phase not illustratedin FIGS. 3A-3J, accordingly it is assumed that drain switches322A(0)-322A(N-1) and 322B(0)-322B(N-1) and leg switches312A(0)-312A(N-1) and 312B(0)-312B(N-1) do not change state in thetransition from the preceding reuse phase (not illustrated in FIGS.3A-3J) to pre-fill phase 300A. In contrast, recycle switches 332A-332Band terminal switches 306A-306B do change state in the transition fromthe preceding reuse phase (not illustrated in FIGS. 3A-3J) to pre-fillphase 300A. A state transition of any switch in general in FIGS. 3A-3J,and in particular recycle switches 332A-332B and terminal switches306A-306B in FIG. 3A, is called out by a stippled ellipse shown underthe state-transitioning switch.

In FIG. 3B, memory device 301 is shown in evaluation phase 302B, whichcorresponds, e.g., to evaluation phase 206A of FIG. 2 .

In evaluation phase 302B, none of the switches change state relative topre-fill phase 302A. However, rather than the precharge circuit (138 inFIG. 1 ) in sense amplifier 303 that was used in pre-fill phase 302A,the evaluation circuit (140 in FIG. 1 ) in sense amplifier 303 is usedin evaluation phase 302B. Hence, evaluation phase 302B is considered tobe a different state than evaluation phase 302A despite the absence ofchanges in switch states between evaluation phase 302B and pre-fillphase 302A.

The resultant charge and the resultant_bar charge on correspondingterminals 304A-304B are compared by the evaluation circuit (140 in FIG.1 ) in sense amplifier 303 in evaluation phase 302B. Based on thecomparison, sense amplifier 303 generates a signal on output terminal304C indicating a particular logic state stored in the memory cellconnected to bit line B_Line(0).

In FIG. 3C, memory device 301 is shown in recover phase 302C, whichcorresponds, e.g., to recover phase 216A of FIG. 2 .

In recover phase 302C, terminal switches 306A-306B are controlled to beopen, thereby disconnecting terminals 304A-304B of sense amplifier 303from corresponding branched lines 309A-309B. Also in recover phase 302C,recycle switches 332A-332B are controlled to be closed, therebyconnecting capacitors 336A-336B to corresponding branched lines309A-309B of the first and second line pairs. First and second chargesare transferred (or ‘recovered’) into capacitors 336A-336Bcorrespondingly from the first line pair (in recover phase 302C,represented by bit line B_Line(0) and branched line 309A) and the secondline pair (in recover phase 302C, represented by bit_bar lineB_bar_Line(0) and branched line 309B).

In FIG. 3D, memory device 301 is shown in drainage phase 302D, whichcorresponds, e.g., to drainage phase 218A of FIG. 2 .

In drainage phase 302D, recycle switches 332A-332B are controlled to beopen, thereby disconnecting capacitors 336A-336B from correspondingbranched lines 309A-309B of the first and second line pairs.Consequently, the first and second charges remain stored in capacitors336A-336B. In contrast to the noted discharge mode of other approaches(see discussion above) which must discharge relatively larger amounts ofcharge, when capacitors 336A-336B are disconnected, relatively smallfirst and second amounts of charge (residual charges) remain on thecorresponding first line pair (in drainage phase 302D, represented bybit line B_Line(0) and branched line 309A) and the second line pair (indrainage phase 302D, represented by bit_bar line B_bar_Line(0) andbranched line 309B).

Also in drainage phase 302D, drain switches 322A(0) and 322B(0) arecontrolled to be closed. Consequently, bit line B_Line(0) (and thus thefirst line pair including branched line 309A) and bit_bar lineB_bar_Line(0) (and thus the second line pair including branched line309B) are connected to ground, which removes the first and secondresidual charges from the first and second line pairs.

In FIG. 3E, memory device 301 is shown in reuse phase 302E, whichcorresponds, e.g., to reuse phase 212B of FIG. 2 .

In reuse phase 302E, drain switches 322A(0) and 322B(0) are controlledto be open. Consequently, bit line B_Line(0) and bit_bar lineB_bar_Line(0) are disconnected from ground. Leg switches 312A(0) and312B(0) are controlled to be open. Consequently, bit line B_Line(0) andbit_bar line B_bar_Line(0) are disconnected from corresponding branchedlines 309A-309B. Leg switches 312A(1) and 312B(1) are controlled to beclosed. Consequently, bit line B_Line(1) and bit_bar line B_bar_Line(1)are connected to corresponding branched lines 309A-309B to form newfirst and second line pairs.

Also in reuse phase 302E, recycle switches 332A-332B are controlled tobe closed, thereby connecting capacitors 336A-336B to correspondingbranched line 309A of the first line pair (and thus, in reuse phase302E, also to bit line B_Line(1)) and branched line 309B of the secondline pair (and thus, in reuse phase 302E, also to bit_bar lineB_bar_Line(1)). Consequently, the first and second charges stored incapacitors 336A-336B are transferred onto the corresponding first andsecond line pairs.

In FIG. 3F, memory device 301 is shown in pre-fill phase 302F, whichcorresponds, e.g., to pre-fill phase 214B of FIG. 2 .

In pre-fill phase 302F, recycle switches 332A-332B are controlled to beopen, thereby disconnecting capacitors 336A-336B from correspondingbranched lines 309A-309B. Also, terminal switches 306A-306B arecontrolled to be closed, thereby connecting terminals 304A-304B of senseamplifier 303 to corresponding branched lines 309A-309B. As such, inpre-fill phase 302F, the precharge circuit (138 in FIG. 1 ) in senseamplifier 304A provides amounts of charge to adjust voltages oncorresponding branched lines 309A-309B to a level of a referencevoltage. Consequently, a resultant charge and a resultant_bar chargeaccumulate on the corresponding branched line 309A of first line pair(and thus, in pre-fill phase 302F, also on bit line B_Line(1)) andbranched line 309B of the second line pair (and thus, in reuse phase302E, also on bit_bar line B_bar_Line(1)).

In FIG. 3G, memory device 301 is shown in evaluation phase 302G, whichcorresponds, e.g., to evaluation phase 206B of FIG. 2 .

In evaluation phase 302G, none of the switches change state relative topre-fill phase 302F. However, rather than the precharge circuit (138 inFIG. 1 ) in sense amplifier 303 that was used in pre-fill phase 302F,the evaluation circuit (140 in FIG. 1 ) in sense amplifier 303 is usedin evaluation phase 302G. Hence, evaluation phase 302G is considered tobe a different state than evaluation phase 302F despite the absence ofchanges in switch states between evaluation phase 302F and pre-fillphase 302G.

The resultant charge and the resultant_bar charge on correspondingterminals 304A-304B are compared by the evaluation circuit (140 in FIG.1 ) in sense amplifier 303 in evaluation phase 302G. Based on thecomparison, sense amplifier 303 generates a signal on output terminal304C indicating a particular logic state stored in the memory cellconnected to bit line B_Line(1).

In FIG. 3H, memory device 301 is shown in recover phase 302H, whichcorresponds, e.g., to recover phase 216B of FIG. 2 .

In recover phase 302H, terminal switches 306A-306B are controlled to beopen, thereby disconnecting terminals 304A-304B of sense amplifier 303from corresponding branched lines 309A-309B. Also in recover phase 302H,recycle switches 332A-332B are controlled to be closed, therebyconnecting capacitors 336A-336B to corresponding branched lines309A-309B of the first and second line pairs. First and second chargesare transferred (or ‘recovered’) into capacitors 336A-336Bcorrespondingly from the first line pair (in recover phase 302H,represented by bit line B_Line(1) and branched line 309A) and the secondline pair (in recover phase 302C, represented by bit_bar lineB_bar_Line(1) and branched line 309B).

In FIG. 3I, memory device 301 is shown in drain or drainage phase 3021,which corresponds, e.g., to drainage phase 218B of FIG. 2 .

In drainage phase 3021, recycle switches 332A-332B are controlled to beopen, thereby disconnecting capacitors 336A-336B from correspondingbranched lines 309A-309B of the first and second line pairs.Consequently, the first and second charges remain stored in capacitors336A-336B. When capacitors 336A-336B are disconnected, relatively smallfirst and second residual charges remain on the corresponding first linepair (in drainage phase 3021, represented by bit line B_Line(1) andbranched line 309A) and the second line pair (in drainage phase 3021,represented by bit_bar line B_bar_Line(1) and branched line 309B).

Also in drainage phase 3021, drain switches 322A(1) and 322B(1) arecontrolled to be closed. Consequently, bit line B_Line(1) (and thus thefirst line pair including branched line 309A) and bit_bar lineB_bar_Line(1) (and thus the second line pair including branched line309B) are connected to ground, which removes the first and secondresidual charges from the first and second line pairs.

In FIG. 3J, memory device 301 is shown in reuse phase 302J, whichcorresponds, e.g., to reuse phase 212A of FIG. 2 .

In reuse phase 302J, drain switches 322A(1) and 322B(1) are controlledto be open. Consequently, bit line B_Line(1) and bit_bar lineB_bar_Line(1) are disconnected from ground. Leg switches 312A(1) and312B(1) are controlled to be open. Consequently, bit line B_Line(1) andbit_bar line B_bar_Line(1) are disconnected from corresponding branchedlines 309A-309B. Leg switches 312A(N-1) and 312B(N-1) are controlled tobe closed. Consequently, bit line B_Line(N-1) and bit_bar lineB_bar_Line(N-1) are connected to corresponding branched lines 309A-309Bto form new first and second line pairs.

Also in reuse phase 302J, recycle switches 332A-332B are controlled tobe closed, thereby connecting capacitors 336A-336B to correspondingbranched line 309A of the first line pair (and thus, in reuse phase302J, also to bit line B_Line(N-1)) and branched line 309B of the secondline pair (and thus, in reuse phase 302J, also to bit_bar lineB_bar_Line(N-1)). Consequently, the first and second charges stored incapacitors 336A-336B are transferred onto corresponding the first andsecond line pairs.

In some embodiments, in reuse phases 302J and 302E and in correspondingpre-fill phases 302A and 302F, leg switches 312A(0)-312A(N-1) and312B(0)-312B(N-1) are controlled to be open.

FIG. 4 is a flowchart of a method 402 of reading a memory cell, inaccordance with at least one embodiment of the present disclosure.

At block 404, the first and second branched lines are pre-boosted. Block404 corresponds, e.g., to pre-boost phases 204A and 204B of FIG. Block404 includes blocks 406 and 408. At block 406, first and second chargesfrom the first and second capacitors are transferred (‘reused’) on thefirst and second branched lines. Block 404 corresponds, e.g., to reusephases 302E and 302J of corresponding FIGS. 3E and 3J. From block 406,flow proceeds to block 408. At block 408, each of the first and secondbranched lines is pre-filled. Block 408 corresponds, e.g., to phases302A and 302F of corresponding FIGS. 3A and 3F. From block 404, flowproceeds to a block 410.

At block 410, the stored value in a memory cell is evaluated by thesense amplifier. Block 410 corresponds, e.g., to phases 206A and 206B ofFIG. 2 . Block 410 includes a block 412. At block 412, the stored valuein a memory cell is evaluated by the sense amplifier based on: aresultant charge (resulting from a combination of reference charge onfirst branched line and a data charge on a bit line); and acorresponding resultant_bar charge (resulting from a combination ofreference charge on second branched line and a data_bar charge on acorresponding bit_bar line). Block 412 corresponds, e.g., to phases 302Band 302G of corresponding FIGS. 3B and 3G. From block 410, flow proceedsto a block 414.

At block 414, charge is discharged from the selected bit line and thecorresponding selected bit_bar line. Block 414 corresponds, e.g., tophases 210A and 210B of FIG. 2 . Block 414 includes blocks 418 and 420.At block 418, first and second charges are transferred (‘recovered’)form the selected bit line and the corresponding selected bit_bar lineinto the corresponding first and second capacitors. Block 418corresponds, e.g., to phases 302C and 302H of corresponding FIGS. 3C and3H. From block 418, flow proceeds to block 420.

At block 420, the selected bit line and the corresponding selectedbit_bar line are drained to ground. Block 420 corresponds, e.g., tophases 202D and 202J of corresponding FIGS. 2D and 2J.

In some embodiments, as noted, read operations 202A-202B are instancesof a cyclic general read cycle. Accordingly, in some embodiments, flowproceeds to loop from block 414 to block 404, as indicated by the dashedline extending from block 414 to block 404.

One of ordinary skill in the art would recognize that operations areable to be removed or that additional operations are able to be added toat least one of the above-noted methods without departing from the scopeof this description. One of ordinary skill in the art would alsorecognize that an order of operations in at least one of the above-notedmethods is able to be adjusted without departing from the scope of thisdescription.

In some embodiments, a method (for recycling charge from a first bitline of a memory device to a second bit line of the memory device)includes: before pre-filling the second bit line, momentarily closingswitches to transfer a first charge from the first bit line which isinvolved in a first read operation to the second bit line which isinvolved subsequently in a second read operation; and each of the firstbit line and the second bit line being served by a same sense amplifier.

In some embodiments, each of the first bit line and the second bit lineis selectively connectable to the sense amplifier via a first branchedline, and the momentarily closing switches to transfer a first chargeincludes: recovering the first charge from the first bit line associatedwith a first memory cell of the memory device, the first charge being aresidual of a preceding first evaluation included as a phase in thefirst read operation, the first evaluation being performed by the senseamplifier; storing the first charge; reusing the first charge to atleast partially charge the first branched line; supplementallypre-filling the first branched line to a reference charge; and using thesense amplifier to make a second evaluation of a stored value in asecond memory cell relative to the reference charge, the secondevaluation being included in the second read operation.

In some embodiments, wherein the recovering includes: connecting thefirst bit line to the branched line to form a line pair; connecting acapacitor to the line pair; and transferring the first charge from theline pair into the capacitor.

In some embodiments, the transferring leaves a residual amount of charge(residual charge) on the line pair, and the recovering further includes:disconnecting the line pair from the capacitor; and reducing theresidual charge on the line pair.

In some embodiments, the reducing includes: connecting the line pairdirectly to ground.

In some embodiments, the recovering includes storing the first charge ina capacitor; and the reusing includes: connecting a second bit line tothe branched line; and transferring the first charge from the capacitoronto the branched line.

In some embodiments, the supplementally pre-filling includes:disconnecting the branched line from the capacitor; connecting thebranched line to a corresponding one of first and second terminals ofthe sense amplifier; and adjusting a charge-level on the branched linefrom the first charge to a reference charge.

In some embodiments, the using the sense amplifier to make a secondevaluation includes: connecting the branched line to the bit line toform a line pair and thereby producing a resultant charge; and comparingthe resultant charge against a reference signal at the sense amplifier.

In some embodiments, a memory device includes: a first bit line; asecond bit line; a branched line; switches for selectively connectingthe first bit line or the second bit line to the branched line; and acontroller configured to generate recycle control signals that controlthe switches to transfer a first charge via the branched line from thefirst bit line which is involved in a first read operation to a secondbit line which is involved subsequently in a second read operationperformed subsequently to the first read operation; and each of thefirst bit line and the second bit line being served by a same senseamplifier.

In some embodiments, the controller is further configured to generaterecycle control signals that control the switches to do as followsincluding: recovering the first charge from a first bit line associatedwith a first memory cell, the first charge being a residual of apreceding first evaluation included as a phase in the first readoperation, the first evaluation being performed by the sense amplifier;and storing the first charge; reusing the first charge to at leastpartially charge the branched line; and supplementally pre-filling thefirst branched line to a reference charge; and wherein the senseamplifier is configured to make a second evaluation of a stored value ina second memory cell relative to the reference charge, the secondevaluation being included in the second read operation.

In some embodiments, the controller is further configured to generaterecycle control signals that control the switches to do as followsincluding: permitting, during the recovering, flow of charge(charge-flow) from the branched line to a capacitor to accumulate thefirst charge; interrupting, during a drainage phase in which the firstcharge is preserved, charge-flow from the branched line to thecapacitor; and permitting, during the reusing, charge-flow from thecapacitor to the branched line.

In some embodiments, the branched line is selectively connectable to afirst terminal of the sense amplifier; during the reusing, thecontroller is further configured to generate recycle control signalsthat control the switches to do as follows including: disconnecting thefirst terminal of the sense amplifier from the branched line; connectinga selected one of the bit lines to the branched line to form a linepair; permitting charge-flow between from the capacitor to the linepair.

In some embodiments, a result of the reusing is that a residual amountof charge (residual charge) remains on the line pair; and during thedrainage phase, the controller is further configured to generate recyclecontrol signals that control the switches to do as follows including:interrupting charge-flow between the line pair and the capacitor; andcausing the residual charge on the line pair to be reduced.

In some embodiments, the memory device further includes: a capacitor;and a recycle switch, a first terminal of the recycle switch beingconnected to a first terminal of the capacitor, and a second terminal ofthe recycle switch being connected to the branched line, and a controlterminal of the recycle switch being connected so as to receive controlsignals from the controller.

In some embodiments, during a pre-fill phase, the controller is furtherconfigured to generate recycle control signals that control the switchesto do as follows including: interrupting charge-flow between thebranched line and a capacitor; and causing the branched line to beconnected to a first terminal of the sense amplifier; and the senseamplifier is configured to do as follows including adjusting acharge-level on the branched line according to the reference charge.

In some embodiments, a method (of reading a memory device) includes:recovering a first charge from a first bit line associated with a firstmemory cell that was a subject of a preceding first evaluation, thefirst evaluation being included as a phase in a first read operation,the first evaluation being performed by a sense amplifier; reusing thefirst charge to at least partially charge a branched line;supplementally pre-filling the branched line to a reference charge;using the sense amplifier to make a second evaluation of evaluating astored value in a second memory cell based on a resultant charge, theresultant charge resulting from a combination of the reference charge onthe branched line and a data charge on a second bit line associated witha second memory cell of the memory device; and the second evaluationbeing included in a second read operation.

In some embodiments, the recovering the first charge includes:connecting the first bit line to the branched line to form a line pair;connecting a capacitor to the line pair; and transferring the firstcharge from the line pair into the capacitor.

In some embodiments, the transferring leaves a residual amount of charge(residual charge) on the line pair; and after the transferring, themethod further comprises: disconnecting the line pair from thecapacitor; and reducing the residual charge on the line pair.

In some embodiments, the reducing includes: connecting the line pairdirectly to ground.

In some embodiments, the recovering recovers the first charge into acapacitor; and the reusing includes: connecting the second bit line tothe branched line; and transferring the first charge from a capacitoronto the branched line.

In some embodiments, the supplementally pre-filling includes:disconnecting the branched line from a capacitor; connecting thebranched line to a corresponding one of first and second terminals ofthe sense amplifier; and adjusting a charge-level on the branched linefrom the first charge to the reference charge.

In some embodiments, the evaluating includes: connecting the branchedline to the bit line to form a line pair and thereby producing theresultant charge; and comparing the resultant charge against a referencesignal at the sense amplifier.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method for recycling charge from a first bitline of a memory device to a second bit line of the memory device, themethod comprising: before pre-filling the second bit line, momentarilyclosing switches to transfer a first charge from the first bit linewhich is involved in a first read operation to the second bit line whichis involved subsequently in a second read operation; and each of thefirst bit line and the second bit line being served by a same senseamplifier.
 2. The method of claim 1, wherein: each of the first bit lineand the second bit line is selectively connectable to the senseamplifier via a first branched line; and the momentarily closingswitches to transfer a first charge includes: recovering the firstcharge from the first bit line associated with a first memory cell ofthe memory device, the first charge being a residual of a precedingfirst evaluation included as a phase in the first read operation, thefirst evaluation being performed by the sense amplifier; storing thefirst charge; reusing the first charge to at least partially charge thefirst branched line; supplementally pre-filling the first branched lineto a reference charge; and using the sense amplifier to make a secondevaluation of a stored value in a second memory cell relative to thereference charge, the second evaluation being included in the secondread operation.
 3. The method of claim 2, wherein the recoveringincludes: connecting the first bit line to the branched line to form aline pair; connecting a capacitor to the line pair; and transferring thefirst charge from the line pair into the capacitor.
 4. The method ofclaim 3, wherein: the transferring leaves a residual amount of charge(residual charge) on the line pair; and the recovering further includes:disconnecting the line pair from the capacitor; and reducing theresidual charge on the line pair.
 5. The method of claim 4, wherein thereducing includes: connecting the line pair directly to ground.
 6. Themethod of claim 2, wherein: the recovering includes: storing the firstcharge in a capacitor; and the reusing includes: connecting a second bitline to the branched line; and transferring the first charge from thecapacitor onto the branched line.
 7. The method of claim 6, wherein thesupplementally pre-filling includes: disconnecting the branched linefrom the capacitor; connecting the branched line to a corresponding oneof first and second terminals of the sense amplifier; and adjusting acharge-level on the branched line from the first charge to a referencecharge.
 8. The method of claim 7, wherein the using the sense amplifierto make a second evaluation includes: connecting the branched line tothe bit line to form a line pair and thereby producing a resultantcharge; and comparing the resultant charge against a reference signal atthe sense amplifier.
 9. A memory device comprising: a first bit line; asecond bit line; a branched line; switches for selectively connectingthe first bit line or the second bit line to the branched line; and acontroller configured to generate recycle control signals that controlthe switches to transfer a first charge via the branched line from thefirst bit line which is involved in a first read operation to a secondbit line which is involved subsequently in a second read operationperformed subsequently to the first read operation; and each of thefirst bit line and the second bit line being served by a same senseamplifier.
 10. The memory device of claim 9, wherein the controller isfurther configured to generate recycle control signals that control theswitches to do as follows including: recovering the first charge from afirst bit line associated with a first memory cell, the first chargebeing a residual of a preceding first evaluation included as a phase inthe first read operation, the first evaluation being performed by thesense amplifier; and storing the first charge; reusing the first chargeto at least partially charge the branched line; and supplementallypre-filling the first branched line to a reference charge; and whereinthe sense amplifier is configured to make a second evaluation of astored value in a second memory cell relative to the reference charge,the second evaluation being included in the second read operation. 11.The memory device of claim 10, wherein the controller is furtherconfigured to generate recycle control signals that control the switchesto do as follows including: permitting, during the recovering, flow ofcharge (charge-flow) from the branched line to a capacitor to accumulatethe first charge; interrupting, during a drainage phase in which thefirst charge is preserved, charge-flow from the branched line to thecapacitor; and permitting, during the reusing, charge-flow from thecapacitor to the branched line.
 12. The memory device of claim 11,wherein: the branched line is selectively connectable to a firstterminal of the sense amplifier; during the reusing, the controller isfurther configured to generate recycle control signals that control theswitches to do as follows including: disconnecting the first terminal ofthe sense amplifier from the branched line; connecting a selected one ofthe bit lines to the branched line to form a line pair; permittingcharge-flow between from the capacitor to the line pair.
 13. The memorydevice of claim 10, further comprising: a capacitor; and a recycleswitch, a first terminal of the recycle switch being connected to afirst terminal of the capacitor, and a second terminal of the recycleswitch being connected to the branched line, and a control terminal ofthe recycle switch being connected so as to receive control signals fromthe controller.
 14. A method of reading a memory device, the methodcomprising: recovering a first charge from a first bit line associatedwith a first memory cell that was a subject of a preceding firstevaluation, the first evaluation being included as a phase in a firstread operation, the first evaluation being performed by a senseamplifier; reusing the first charge to at least partially charge abranched line; supplementally pre-filling the branched line to areference charge; and using the sense amplifier to make a secondevaluation of evaluating a stored value in a second memory cell based ona resultant charge, the resultant charge resulting from a combination ofthe reference charge on the branched line and a data charge on a secondbit line associated with a second memory cell of the memory device; andthe second evaluation being included in a second read operation.
 15. Themethod of claim 14, wherein the recovering the first charge includes:connecting the first bit line to the branched line to form a line pair;connecting a capacitor to the line pair; and transferring the firstcharge from the line pair into the capacitor.
 16. The method of claim15, wherein: the transferring leaves a residual amount of charge(residual charge) on the line pair; and after the transferring, themethod further comprises: disconnecting the line pair from thecapacitor; and reducing the residual charge on the line pair.
 17. Themethod of claim 16, wherein the reducing includes: connecting the linepair directly to ground.
 18. The method of claim 14, wherein: therecovering recovers the first charge into a capacitor; and the reusingincludes: connecting the second bit line to the branched line; andtransferring the first charge from a capacitor onto the branched line.19. The method of claim 18, wherein the supplementally pre-fillingincludes: disconnecting the branched line from a capacitor; connectingthe branched line to a corresponding one of first and second terminalsof the sense amplifier; and adjusting a charge-level on the branchedline from the first charge to the reference charge.
 20. The method ofclaim 19, wherein the evaluating includes: connecting the branched lineto the bit line to form a line pair and thereby producing the resultantcharge; and comparing the resultant charge against a reference signal atthe sense amplifier.